My object is missing when i turn on alpha
According to your file, the problem is you are trying to use Cycles material node as BI material node, which cannot happen.



Solution:


Switch the Render engine from Blender Render to Cycles;
If you want to render it in Blender Render (BI), you have to either toggle off the Use Node button, or create a new material node readable for BI.


I assume the first one is your better option, since it seems you sort of mis-switched the engine at some point (or the material node is appended from anywhere else).